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The Polymerase Chain Reaction (PCR)


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The polymerase chain reaction (PCR) is a process for amplifying very tiny amounts of DNA such that they can be visualized and assessed or used in further scientific processes. PCR is widely used in almost all branches of biology including molecular biology, microbiology, genetics, environmental science, food science, biotechnology, forensic science, and clinical diagnostics. The PCR technique involves using an enzyme called DNA polymerase to amplify (duplicate many times) a piece of DNA. The original molecule of DNA is duplicated by the DNA polymerase enzyme, thus doubling the number of DNA molecules.

Then each of these molecules is duplicated in a second cycle of replication, resulting in four molecules. Again, each of these molecules is duplicated by the enzyme in a third cycle of replication. The process is referred to as a chain reaction - hence the name “polymerase chain reaction". The original single piece of DNA is amplified over many cycles, generating millions of copies of the original DNA molecule. Often the PCR experiment is performed simply to verify the presence or absence of a particular type of DNA but sometimes PCR is used to generate sufficient DNA to be used in a subsequent experiment, for example cloning or DNA sequencing. The original PCR process has been extensively modified to perform a wide array of genetic manipulations, diagnostic tests, and for many other uses. (Reference: Real-Time PCR: Current Technology and Applications ISBN: 978-1-904455-39-4)

Modern variations of PCR include Real-time PCR. This technology allows the newly generated DNA molecules to be analysed immediately they are produced. This ability to monitor the PCR process in real time, while the reaction is still occuring, is of enormous benefit to scientists as it reduces the amount of time required to generate a result (especially important in clinical diagnostics) and also enables the quantitation of the DNA. Real-time PCR can not only answer the question “what DNA is present?" but also “how much DNA is present?".

The polymerase chain reaction is used by a huge number of scientists in a vast range of scientific disciplines. In microbiology and molecular biology laboratories, for example, PCR is used in DNA cloning experiments, genetic manipulation, DNA sequencing, genetic modification, and many other procedures. In clinical diagnostic laboratories PCR is used for the diagnosis of microbial infections, the detection of hereditary diseases and in epidemiological studies. In medicine PCR has led to significant improvements in the diagnosis of infectious disease. PCR is also used for genetic fingerprinting in forensic and paternity testing laboratories. (Reference: Real-Time PCR in Microbiology: From Diagnosis to Characterization ISBN: 978-1-904455-18-9)

The latest developments in PCR can be found in the new publication Real-Time PCR - Current Technology and Applications. Topical science issues and details of new technology at the Molecular Biology Blog .


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